Cytokines are polypeptide hormones that are produced by a cell and affect cell growth or metabolism in either autocrine, paracrine or endocrine fashion. Cytokines are physicochemically diverse, ranging in size from 5 kDa (TGF-α) to 140 kDa (Mullerian-inhibiting substance). Structurally, cytokines include a group distinguished by their four-helix bundle conformation. They include single polypeptide chains, as well as disulfide-linked homodimers and heterodimers.
The IL-12 family of cytokines is involved in immunomodulatory activities. Proteins in the L-12 family are heterodimers and include IL-12, IL-23 and IL-27. IL-12 is a heterodimer comprising a p35 and p40 subunit (Kobayashi et al., J. Exp. Med. 170:827–845, 1989), IL-23 comprises p19 and p40 subunits (Oppman et al., Immunity 13:715–725, 2000), and IL-27 heterodimer comprises subunits p28 and Epstein Barr virus-induced protein 3 (EBI3; Pflanz et al., Immunity 16:779–790, 2002).
In view of the proven clinical utility of cytokines, there is a need in the art for additional such molecules for use as both therapeutic agents and research tools and reagents. Cytokines are used in the laboratory to study developmental processes, and in laboratory and industry settings as components of cell culture media.